This invention relates to engine exhaust baffles for water-craft, and more particularly to an improved apparatus for diffusing the exhaust flow of a gas turbine engine and for preventing intrusion of water into the turbine through the exhaust duct.
Various watercraft, such as surface effect, air cushion, or hydrofoil vessels are powered by gas turbines or other engines that produce a large volume of exhaust gas that is ducted for overboard discharge. In some of these, the discharge is effected at locations and levels close enough to the waterline of the craft or vessel that ingestion or intrusion of water, with resulting catastrophic damage to the engine, becomes a distinct possibility. This is particularly true where the exhaust ducts discharge through ports in the sides or stern of the vessel or craft and the craft is operated at times under circumstances, such as in following seas or when manuevering alongside a ship, that wave and vessel action can slosh or pump water into the exhaust ports and come into contact with turbine blades which are running at temperatures in excess of 1000.degree. F. Present systems attempt to reduce the problem by utilizing long exhaust ducting including a right angle bend just prior to exhaust discharge which significantly reduces usable horsepower by increasing back pressure.
A variety of deflector devices have been provided for a variety of purposes in the engine exhaust streams of certain water and aircraft. U.S. Pat. Nos. 4,007,587 and 4,099,375 disclose examples of vane structures located in, or at the termination of, exhaust ducts of turbine engine powered aircraft such as helicopters for the principal purpose of reducing the exhaust plume and infrared radiation of the exhaust gases and duct structure. U.S. Pat. Nos. 1,469,796 and 2,444,318 disclose diffusion vane structures in the exhaust paths of aircraft in order to enhance their capability of skimming on or over the surface of a body of water.
An exhaust gas deflecting baffle device is disclosed by U.S. Pat. No. 3,130,541 for use in through the stern exhaust pipes of inboard powered boats. That baffle device serves to cool the exhaust gases so as to minimize the tendency thereof to rise and be drawn forward over the stern of the boat.
The foregoing devices, while having exhaust gas diffusing functions in combination with turbine and other engine powered craft, do not address the problem of excluding water that impinges against the craft so as to tend to be driven into the exhaust duct. Accordingly, there exists a need for a simple, inexpensive, and yet effective device for not only diffusing the exhaust of a turbine engine in a watercraft, but also for excluding or rejecting impinging water which would otherwise enter through the exhaust duct and be likely to damage the turbine.
Of course, the introduction of any device in the exhaust system that would produce a material or significant increase in exhaust back-pressure as seen by the engine would also materially reduce the power output available from that engine as well as the operating efficiency thereof. Accordingly, it is desirable that a diffuser or baffle device, if it is to be used in conjunction with an engine exhaust system, be such as to offer little or no back-pressure to the exhaust stream.